Increase in B-cell-activation factor (BAFF) and IFN-γ productions by tonsillar mononuclear cells stimulated with deoxycytidyl-deoxyguanosine oligodeoxynucleotides (CpG-ODN) in patients with IgA nephropathy

IgA nephropathy (IgAN), the most common form of primary glomerulonephritis, is recognized as a tonsil-related diseases since it often gets worse after and/or during acute tonsillitis and the disease progression is often prevented by tonsillectomy. Although several reports showed an increase in IgA production of tonsillar mononuclear cells (TMCs), its mechanism has not yet been fully clarified. Recently, B-cell-activation factor (BAFF), which stimulates B-cell proliferation and immunoglobulin production, was identified. Unmethylated deoxycytidyl-deoxyguanosine oligodeoxynucleotide (CpG-ODN), which is able to mimic the immunostimulatory activity of microbial DNA, is known to be involved in the production of immunoglobulins and some cytokines. In this study, we focused on roles of BAFF and IFN-γ in IgA production of TMCs stimulated with CpG-ODN in IgAN patients. Two-color flow cytometric analysis revealed that the intercellular expression of IFN-γ on the T-cells freshly isolated from tonsils was significantly higher in IgAN patients than in non-IgAN patients (p = 0.032). The spontaneous productions of IgA and IFN-γ of TMCs were significantly higher in IgAN patients than in non-IgAN patients (p = 0.023 and p = 0.02). Under stimulation with CpG-ODN, the productions of IgA, BAFF and IFN-γ of TMCs were significantly higher in IgAN patients than in non-IgAN patients (p = 0.013, p = 0.005 and p = 0.039). The IgA production of TMCs stimulated by CpG-ODN was inhibited by the treatment with anti-BAFF antibody and/or anti-IFN-γ antibody. Under stimulation with IFN-γ, the BAFF expression on the CD1c cells and the BAFF production of TMCs were significantly higher in IgAN patients than in non-IgAN patients (p = 0.004 and p = 0.042). These data suggest that hyper-immune response to microbial DNA may be present in IgAN patients and may lead to hyperproduction of BAFF up-regulated by IFN-γ, resulting in hyperproduction of IgA in IgAN patients.